The invention relates to electric metal film resistors having a nickel alloy as a resistance material.
Such resistors are known from GB-PS 1,338,735 having an Ni-Cr-Al alloy as a resistance material, in which EQU 15.ltoreq.Ni.ltoreq.55 EQU 10.ltoreq.Cr.ltoreq.68 and EQU 2.ltoreq.Al.ltoreq.60,
expressed in % by weight.
These resistors which are manufactured by providing the alloy on a substrate surface by sputtering and then stabilising them by heating them in an oxygen-containing atmosphere and which have resistance values be are readily produced on an industrial scale from approximately 5 Ohm to 1 M Ohm. They have a temperature coefficient of the electric resistance with a value between .+-.25.times.10.sup.-6 /.degree.C. in the temperature range from -55.degree. to +155.degree. C.
Resistors of this material with a value below 5 Ohm can be made by sputtering, it is true, but then it is necessary to sputter for a very long period of time, for example, for 10 hours, to obtain a resistor of 0.5 Ohm and for this purpose a power of 8 kW per 40,000 pieces is necessary. In practice this is not acceptable. For this value it has therefore been endeavoured to use nickel-phosphorus as a resistance material which is deposited on a nucleated substrate by means of an electroless nickel plating bath. The quality requirements which are used for resistors above 5 Ohm manufactured by sputtering, can by no means be realised by means of these electroless nickel plated resistors.
Resistance bodies for applications in which high powers (&gt;1W) are dissipated may reach a temperature of approximately 300.degree. C. during operation. However, they must remain stable also after a long period in use in which said operating temperature is reached several times, is maintained for some time, after which the resistance body is again cooled to room temperature. Another category of low ohmic resistors are the so-called precision resistors. These resistors must have a temperature coefficient of the resistance value between .+-.25.times.10.sup.-6 /.degree.C.
Furthermore, the layer provided by sputtering must have a high resistance to detrition. Sputtering as a matter of fact takes place in a rotating drum in which the carriers to be coated can move freely and rub along each other with some force. When the layer consists of a material having a low resistance to detrition this means that the sputtering time is prolonged as a result of the detrition and moreover that the homogeneity of the deposition is disturbed and hence the appearance of the products is deteriorated.
The known resistance materials which are provided by sputtering, for example the above mentioned Ni-Cr-Al alloy, but also alloys of Ni-Cr or Ni-Cu, cannot satisfy all these requirements.
Ni-Cr, for example, has a lower level of the resistivity than an Ni-Cr-Al alloy but a temperature coefficient of the resistance of approximately 140.times.10.sup.-6 /.degree.C. Both alloys have a rather low resistance to detrition.
Another binary alloy, Ni Cu, having a low resistivity, cannot be used either. Ni Cu (30/70% by weight) can be sputtered by means of a magnetron sputtering apparatus, but it proved to have a temperature coefficient of the resistance of 100-150.times.10.sup.-6 /.degree.C. and moreover a great variation upon ageing. A lot of dust is formed during the sputtering as a result of the high detrition in the drum and the layer has a poor bonding to the ceramic.